If
the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule
13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following
box ¨.

Note: Schedules
filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See
§ 240.13d-7 for other parties to whom copies are to be sent.

1
The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to
the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided
in a prior cover page.

The information required
on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities
Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject
to all other provisions of the Act (however, see the Notes).

CUSIP NO. 67091U102

1

NAME OF REPORTING PERSON

Etude Capital LLC

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

WC

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

TEXAS

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

28,000

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

- 0 -

PERSON WITH

9

SOLE DISPOSITIVE POWER

28,000

10

SHARED DISPOSITIVE POWER

- 0 -

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

28,000

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

Less than 1%

14

TYPE OF REPORTING PERSON

OO

2

CUSIP NO. 67091U102

1

NAME OF REPORTING PERSON

CapLab Partners LP

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

WC

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

TEXAS

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

163,354

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

- 0 -

PERSON WITH

9

SOLE DISPOSITIVE POWER

163,354

10

SHARED DISPOSITIVE POWER

- 0 -

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

163,354

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

Less than 1%

14

TYPE OF REPORTING PERSON

PN

3

CUSIP NO. 67091U102

1

NAME OF REPORTING PERSON

Capital Laboratories Inc.

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

AF

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

TEXAS

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

163,354

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

- 0 -

PERSON WITH

9

SOLE DISPOSITIVE POWER

163,354

10

SHARED DISPOSITIVE POWER

- 0 -

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

163,354

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

Less than 1%

14

TYPE OF REPORTING PERSON

CO

4

CUSIP NO. 67091U102

1

NAME OF REPORTING PERSON

Steven I. Stein

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

AF

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

USA

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

191,354

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

- 0 -

PERSON WITH

9

SOLE DISPOSITIVE POWER

191,354

10

SHARED DISPOSITIVE POWER

- 0 -

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

191,354

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

Less than 1%

14

TYPE OF REPORTING PERSON

IN

5

CUSIP NO. 67091U102

1

NAME OF REPORTING PERSON

BLR Partners LP

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

WC

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

TEXAS

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

600,000

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

- 0 -

PERSON WITH

9

SOLE DISPOSITIVE POWER

600,000

10

SHARED DISPOSITIVE POWER

- 0 -

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

600,000

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

2.97%

14

TYPE OF REPORTING PERSON

PN

6

CUSIP NO. 67091U102

1

NAME OF REPORTING PERSON

BLRPart, LP

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

AF

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

TEXAS

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

600,000

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

- 0 -

PERSON WITH

9

SOLE DISPOSITIVE POWER

600,000

10

SHARED DISPOSITIVE POWER

- 0 -

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

600,000

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

2.97%

14

TYPE OF REPORTING PERSON

PN

7

CUSIP NO. 67091U102

1

NAME OF REPORTING PERSON

BLRGP Inc.

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

AF

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

TEXAS

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

600,000

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

- 0 -

PERSON WITH

9

SOLE DISPOSITIVE POWER

600,000

10

SHARED DISPOSITIVE POWER

- 0 -

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

600,000

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

2.97%

14

TYPE OF REPORTING PERSON

CO

8

CUSIP NO. 67091U102

1

NAME OF REPORTING PERSON

Fondren Management, LP

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

AF

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

TEXAS

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

600,000

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

- 0 -

PERSON WITH

9

SOLE DISPOSITIVE POWER

600,000

10

SHARED DISPOSITIVE POWER

- 0 -

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

600,000

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

2.97%

14

TYPE OF REPORTING PERSON

PN

9

CUSIP NO. 67091U102

1

NAME OF REPORTING PERSON

FMLP Inc.

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

AF

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

TEXAS

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

600,000

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

- 0 -

PERSON WITH

9

SOLE DISPOSITIVE POWER

600,000

10

SHARED DISPOSITIVE POWER

- 0 -

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

600,000

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

2.97%

14

TYPE OF REPORTING PERSON

CO

10

CUSIP NO. 67091U102

1

NAME OF REPORTING PERSON

The Radoff Family Foundation

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

WC

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

TEXAS

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

517,500

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

- 0 -

PERSON WITH

9

SOLE DISPOSITIVE POWER

517,500

10

SHARED DISPOSITIVE POWER

- 0 -

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

517,500

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

2.6%

14

TYPE OF REPORTING PERSON

CO

11

CUSIP NO. 67091U102

1

NAME OF REPORTING PERSON

Bradley L. Radoff

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

AF, PF

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

USA

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

1,232,500

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

- 0 -

PERSON WITH

9

SOLE DISPOSITIVE POWER

1,232,500

10

SHARED DISPOSITIVE POWER

- 0 -

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

1,232,500*

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

6.1%

14

TYPE OF REPORTING PERSON

IN

* Includes 115,000 Shares owned
directly.

12

CUSIP NO. 67091U102

The following constitutes
Amendment No. 2 to the Schedule 13D filed by the undersigned (“Amendment No. 2”). This Amendment No. 2 amends the Schedule
13D as specifically set forth herein.

Item 3.

Source and Amount of Funds or Other Consideration.

Item 3 is hereby amended
and restated to read as follows:

The Shares purchased
by BLR Partners and Radoff Foundation were purchased with working capital (which may, at any given time, include margin loans
made by brokerage firms in the ordinary course of business) in open market purchases, except as otherwise noted. The aggregate
purchase price of the 600,000 Shares owned directly by BLR Partners is approximately $611,989, including brokerage commissions.
The aggregate purchase price of the 517,500 Shares owned directly by Radoff Foundation is approximately $599,867, including brokerage
commissions.

The Shares directly
owned by Mr. Radoff were purchased with personal funds (which may, at any given time, include margin loans made by brokerage firms
in the ordinary course of business) in open market purchases, except as otherwise noted. The aggregate purchase price of the 115,000
Shares directly owned by Mr. Radoff is approximately $137,470, including brokerage commissions.

The Shares purchased
by Etude and CapLab were purchased with working capital (which may, at any given time, include margin loans made by brokerage firms
in the ordinary course of business) in open market purchases, except as otherwise noted. The aggregate purchase price of the 28,000
Shares owned directly by Etude is approximately $31,640, including brokerage commissions. The aggregate purchase price of the 163,354
Shares owned directly by CapLab is approximately $170,052, including brokerage commissions.

Item 5.

Interest in Securities of the Issuer.

Items 5(a)-(c) are
hereby amended and restated to read as follows:

The aggregate percentage
of Shares reported owned by each person named herein is based upon 20,172,392 Shares outstanding as of November 13, 2017, which
is the total number of Shares outstanding as reported in the Issuer’s Quarterly Report on Form 10-Q, filed with the Securities
and Exchange Commission on November 13, 2017.

A.

Etude

(a)

As of the close of business on December 18, 2017, Etude beneficially owned 28,000 Shares.

Percentage: Less than
1%

(b)

1. Sole power to vote or direct vote: 28,000
2. Shared power to vote or direct vote: 0
3. Sole power to dispose or direct the disposition: 28,000
4. Shared power to dispose or direct the disposition: 0

(c)

The transactions in the Shares by Etude during the past sixty days are set forth in Schedule B
and are incorporated herein by reference.

13

CUSIP NO. 67091U102

B.

CapLab

(a)

As of the close of business on December 18, 2017, CapLab beneficially owned 163,354 Shares.

Percentage: Less than
1%

(b)

1. Sole power to vote or direct vote: 163,354
2. Shared power to vote or direct vote: 0
3. Sole power to dispose or direct the disposition: 163,354
4. Shared power to dispose or direct the disposition: 0

(c)

The transactions in the Shares by CapLab during the past sixty days are set forth in Schedule B
and are incorporated herein by reference.

C.

CapGP

(a)

CapGP, as the general partner of CapLab, may be deemed the beneficial owner of the 163,354 Shares
owned by CapLab.

Percentage: Less than
1%

(b)

1. Sole power to vote or direct vote: 163,354
2. Shared power to vote or direct vote: 0
3. Sole power to dispose or direct the disposition: 163,354
4. Shared power to dispose or direct the disposition: 0

(c)

CapGP has not entered into any transactions in the Shares during the past sixty days. The transactions
in the Shares on behalf of CapLab during the past sixty days are set forth in Schedule B and are incorporated herein by reference.

D.

Mr. Stein

(a)

Mr. Stein, as the President of Etude and the President and sole director of CapGP, may be deemed
the beneficial owner of the (i) 28,000 Shares owned by Etude and (ii) 163,354 Shares owned by CapLab.

Percentage: Less than
1%

(b)

1. Sole power to vote or direct vote: 191,354
2. Shared power to vote or direct vote: 0
3. Sole power to dispose or direct the disposition: 191,354
4. Shared power to dispose or direct the disposition: 0

(c)

Mr. Stein
has not entered into any transactions in the Shares
during the past sixty days. The transactions in the Shares on behalf of Etude and CapLab during the past sixty days are set forth
in Schedule B and are incorporated herein by reference.

14

CUSIP NO. 67091U102

E.

BLR Partners

(a)

As of the close of business on December 18, 2017, BLR Partners beneficially owned 600,000 Shares.

Percentage: Approximately
2.97%

(b)

1. Sole power to vote or direct vote: 600,000
2. Shared power to vote or direct vote: 0
3. Sole power to dispose or direct the disposition: 600,000
4. Shared power to dispose or direct the disposition: 0

(c)

BLR Partners has not entered into any transactions in the Shares during the past sixty days.

F.

BLRPart GP

(a)

BLRPart GP, as the general partner of BLR Partners, may be deemed the beneficial owner of the 600,000
Shares owned by BLR Partners.

Percentage: Approximately
2.97%

(b)

1. Sole power to vote or direct vote: 600,000
2. Shared power to vote or direct vote: 0
3. Sole power to dispose or direct the disposition: 600,000
4. Shared power to dispose or direct the disposition: 0

(c)

BLRPart GP has not entered into any transactions in the Shares during the past sixty days.

G.

BLRGP

(a)

BLRGP, as the general partner of BLRPart GP, may be deemed the beneficial owner of the 600,000
Shares owned by BLR Partners.

Percentage: Approximately
2.97%

(b)

1. Sole power to vote or direct vote: 600,000
2. Shared power to vote or direct vote: 0
3. Sole power to dispose or direct the disposition: 600,000
4. Shared power to dispose or direct the disposition: 0

(c)

BLRGP has not entered into any transactions in the Shares during the past sixty days.

H.

Fondren Management

(a)

Fondren Management, as the investment manager of BLR Partners, may be deemed the beneficial owner
of the 600,000 Shares owned by BLR Partners.

Percentage: Approximately
2.97%

(b)

1. Sole power to vote or direct vote: 600,000
2. Shared power to vote or direct vote: 0
3. Sole power to dispose or direct the disposition: 600,000
4. Shared power to dispose or direct the disposition: 0

15

CUSIP NO. 67091U102

(c)

Fondren Management has not entered into any transactions in the Shares during the past sixty days.

I.

FMLP

(a)

FMLP, as the general partner of Fondren Management, may be deemed the beneficial owner of the 600,000
Shares owned by BLR Partners.

Percentage: Approximately
2.97%

(b)

1. Sole power to vote or direct vote: 600,000
2. Shared power to vote or direct vote: 0
3. Sole power to dispose or direct the disposition: 600,000
4. Shared power to dispose or direct the disposition: 0

(c)

FMLP has not entered into any transactions in the Shares during the past sixty days.

J.

Radoff Foundation

(a)

As of the close of business on December 18, 2017, Radoff Foundation beneficially owned 517,500
Shares.

Percentage: Approximately
2.6%

(b)

1. Sole power to vote or direct vote: 517,500
2. Shared power to vote or direct vote: 0
3. Sole power to dispose or direct the disposition: 517,500
4. Shared power to dispose or direct the disposition: 0

(c)

The transactions in the Shares by Radoff Foundation during the past sixty days are set forth in
Schedule B and are incorporated herein by reference.

K.

Mr. Radoff

(a)

As of the close of business on December 18, 2017, Mr. Radoff directly owned 115,000 Shares. Mr.
Radoff, as the sole shareholder and sole director of each of BLRGP and FMLP and a director of Radoff Foundation, may be deemed
the beneficial owner of the (i) 600,000 Shares owned by BLR Partners and (ii) 517,500 Shares owned by Radoff Foundation.

Percentage: Approximately
6.1%

(b)

1. Sole power to vote or direct vote: 1,232,500
2. Shared power to vote or direct vote: 0
3. Sole power to dispose or direct the disposition: 1,232,500
4. Shared power to dispose or direct the disposition: 0

(c)

The transactions in the Shares by Mr. Radoff during the past sixty days are set forth in Schedule
B and are incorporated herein by reference

16

CUSIP NO. 67091U102

The Reporting Persons,
as members of a “group” for the purposes of Section 13(d)(3) of the Securities Exchange Act of 1934, as amended, may
be deemed the beneficial owner of the Shares directly owned by the other Reporting Persons. Each Reporting Person disclaims beneficial
ownership of such Shares except to the extent of his or its pecuniary interest therein.

17

CUSIP NO. 67091U102

SIGNATURES

After reasonable inquiry
and to the best of his or its knowledge and belief, each of the undersigned certifies that the information set forth in this statement
is true, complete and correct.